Various electronic devices have been used in daily life in accordance with the development of semiconductor and communication technologies. Among the various electronic devices, a display device, which can view and listen to multimedia, has been used most widely. Particularly, technologies in which a plurality of displays are used have been used to use a wider screen in one display device. For example, there is a dual monitor in which two monitors are connected to one PC (personal computer).
Also, studies of a display device that includes a flexible display have been recently made to provide a larger display while maintaining portability of a portable device. For example, there is a display device in which a flexible display is rolled in a rollable display. The display device may extend a screen by unfolding the rollable display if necessary while using a main display.
In such a display device, the rollable display may have various unfolded lengths depending on intention of a user. In this case, it is required to determine which one of applications executed in the display device should be displayed on the rollable display or a size of an application execution screen displayed on the rollable display.